Devices using various types of media such as optical discs, magnetic optical discs, and flexible magnetic disk are known in the art as data storage devices. Among them, hard disk drives (hereinafter referred to as HDDs) have become popular as storage devices for computers to such an extent that they are one of the storage devices indispensable for today's computer systems. Further, not limited to the computers as described above, HDDs are becoming more and more widely used in various applications. For example, HDDs are used for video recording/reproducing devices, car navigation systems, cellular phones, and removable memories for use in digital cameras.
A magnetic disk for HDD has a plurality of data tracks formed in a concentric manner. Each data track holds a plurality of pieces of servo data containing address information and a plurality of data sectors including user data. A plurality of data sectors are recorded between each piece of servo data and the next. An actuator is driven to rotate by a voice coil motor (VCM). A head element unit of a head slider supported by the actuator accesses a desired data sector in accordance with address information in servo data. This allows data to be written to and read from the data sector.
When the magnetic disk is not rotating, the actuator and the slider head are retracted to their parking positions. Load/unload and CSS (Contact Start Stop) systems are known methods to retract the head slider. During the travel between the parking position and a position over the magnetic disk, the HDD controls the VCM speed to control the rotation of the actuator. More specifically, a VCM speed detection circuit detects the VCM speed based on a counter electromotive voltage of the VCM. A controller supplies the VCM with a VCM current so as to bring the detected VCM speed equal to a target speed. detects a first counter electromotive voltage generated by a first current caused to flow through the voice coil motor, with the actuator positioned in place. Further, the detection circuit detects a second counter electromotive voltage generated by a second current, different from the first current, caused to flow through the voice coil motor, with the actuator positioned in place. The controller controls the drive of the actuator using the value obtained by correcting the output of the detection circuit. Further, the controller determines a correction factor for the output of the detection circuit using the first and second counter electromotive voltages. If the correction factor falls outside a reference limit, the controller determines a new circuit parameter for the detection circuit and a new correction factor appropriate to the new circuit parameter. The controller determines the new circuit parameter of the detection circuit and the new correction factor appropriate to the new circuit parameter to prevent unstable VCM speed control that may be caused by the correction factor outside the reference limits.
Embodiments of the present invention are particularly useful when the controller controls the actuator by correcting the output of the detection circuit, into which the new circuit parameter has been set, using the new correction factor, so as to move the head to its parking position. In one aspect, the controller determines the new circuit parameter using the correction factor determined based on the first and second counter electromotive voltages. This ensures more accurate determination of the circuit parameter so as to bring the correction factor closer to a desired value.
In one embodiment, the detection circuit, into which the new circuit parameter has been set, detects a third counter electromotive voltage generated by a third current caused to flow through the voice coil motor, with the actuator positioned in place. The detection circuit may also detect a fourth counter electromotive voltage generated by a fourth current, different from the third current, caused to flow through the voice coil motor, with the actuator positioned in place. In one aspect, the controller determines the new correction factor based on the third and fourth counter electromotive voltages. Measurement of the third and fourth counter electromotive voltages ensures higher accuracy in determining the new correction factor. Here, the value of the third current may be the same as or different from that of the first current. Similarly, the value of the fourth current may be the same as or different from that of the second current.
According to an embodiment of the present invention, the detection circuit detects the first counter electromotive voltage when the actuator follows a first track on the disk and detects the second counter electromotive voltage when the actuator follows a second track different from the first track. In one embodiment, the detection circuit detects the third counter electromotive voltage when the actuator follows a third track on the disk and detects the fourth counter electromotive voltage when the actuator follows a fourth track different from the third track. In one aspect, this makes it possible to prevent generation of sounds. It should be noted that the third track may be the same as or different from the first track. Similarly, the fourth track may be the same as or different from the second track.
In one embodiment, the controller determines, based on the first and second currents and the first and second counter electromotive voltages, a slope of change of the counter electromotive voltage with respect to the current, and use the slope as the correction factor. The controller may determine the new circuit parameter so as to reduce the slope. In one aspect, this makes it possible to prevent unstable VCM speed control that may be caused by a large slope.
In an embodiment, a disk drive of the present invention is provided with a setting circuit adapted to automatically set the circuit parameter. In one aspect, the detection circuit detects the first and second counter electromotive voltages using the circuit parameter set by the setting circuit. The controller may set the new circuit parameter into the detection circuit. In one aspect, this ensures fast calibration with the setting circuit and minimizes unstable operation with the new circuit parameter.
Another embodiment of the present invention is a calibration method to control the speed of the voice coil motor in a disk drive provided with an actuator adapted to support a head and a voice coil motor adapted to drive the actuator. In one embodiment, this method supplies the voice coil motor with a first current to position the actuator in place and detects a first counter electromotive voltage of the voice coil with the actuator positioned in place. The method further supplies the voice coil motor with a second current different from the first current to position the actuator in place and detects a second counter electromotive voltage of the voice coil with the actuator positioned in place. Next, the method determines, based on the first and second counter electromotive voltages, a correction factor for a counter electromotive voltage detected during the speed control. Further, the method sets a new circuit parameter into a detection circuit adapted to detect the counter electromotive voltage of the voice coil motor if the correction factor falls outside a reference limit. The method still further determines a new correction factor appropriate to the new circuit parameter.
For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.